The cutter provided by the instant invention finds particular utility in the authorized opening of cylindrical locks of the horizontal-tumbler type in the event of loss of the key, for example. Such locks are used primarily in coin-operated machines because they provide substantially maximum security, being extremely difficult to pick, even by expert locksmiths. An especially well-known lock of this type is the "Ace", manufactured by the Chicago Lock Co. of Chicago, Ill. The keys for these locks bear the U.S. Pat. No. 1,984,202.
Basically, a lock of this type is cylindrical in construction and has an internal fixed part and a key-operated core or spindle that is angularly movable relative to the fixed part when the proper key actuates the tumbler mechanism to clear the tumblers from the radial interface between the fixed and movable parts. In a typical lock of this type there are seven sets of horizontal tumblers. Each is movable axially to clear the interface by means of a pin that is pushed by a projection of predetermined design on the front end of the tubular key. The pins are of different lengths, as are the key projections, the principle of operation being that the key will push all pins axially in their respective amounts until all tumblers just clear the interface, following which the key can turn the movable part relative to the fixed part and the lock will open.
The key-receiving core faces outwardly and is surrounded by an annular, fixed lock portion which prevents easy access to the tumblers except by the key or a rather complicated pick. There is an annular gap between the core and the annulus for receiving the tubular front end of the key, but this provides only limited working space for a locksmith using a pick.
According to the present invention, a rotary cutter is specially designed to pilot on the core in the annular gap just referred to. The cutter has circumferentially spaced cutting edges designed to cut away the annulus and thus to expose the tumbler pins. These pins may be easily removed, as by so-called needle-nose pliers, following which another special tool, in the form of a depressor, is used to move the tumblers axially to the rear in equal amounts so as to clear the interface, whereupon the depressor acts as a key in the sense that it can be used to turn the core or movable part of the lock. In a case where the lock has seven tumblers, the depressor has seven pins of a length equal to the axial thickness of the radial flange on the movable part into which the tumblers enter under spring loading as is typical of locks of this type. There is thus provided a quick, inexpensive and simple systen of opening locks of this type.